Pit prop with self-centering cap



Feb. 4, 1969 R. BORE PIT PROP WITH SELF-CENTERING CAP Filed April 11, 1967 Q a an INVENTOR 233;

ATTOR United States Patent Ofi ice 3,425,656 Patented Feb. 4, 1969 3,425,656 PIT PROP WITH SELF-CENTERING CAP Raymond Bore, Saint-Etienne, France, assignor to Bennes Marrel, Saint-Etienne, France, a French joint-stock company Filed Apr. 11, 1967, Ser. No. 630,053 Claims priority, application France, Apr. 15, 1966,

US. Cl. 248-357 Int. 01. E04g 25/00; 1221a 15/55 4 Claims ABSTRACT OF THE DISCLOSURE The present invention concerns improvements in or relating to props of the type used in mines for supporting purposes. It concerns, more particularly although not exclusively, a progressive supporting type of hydraulically operated prop.

It is known that at the time they are placed in position, pit props are locked between the floor and roof of a seam, perpendicularly to the mean direction thereof. They are supported on the floor by a sole and on the roof by a cap. In the course of working the seam, relative movement of the floor and roof causes a more or less sharp incline of the body of the prop relatively to the sole and the cap. In the case of progressive support, it is known that the prop is periodically released in order to displace it forward at the same rate as the gantry or cutter advances. When the prop is released, the prop body occupies a position at an angle relatively to the sole. Devices are known capable of ensuring automatic re-aligning of props in order to return them to positions perpendicular to their soles. The invention concerns a device capable of ensuring the re-aligning of a prop cap in order to return it automatically perpendicular to the prop body as soon as the prop is released.

A device according to the invention is characterised by the feature that it comprises a torsion and flexion bar disposed parallel to the longitudinal direction of the cap on which it is fixed by one end, whilst its other end is fitted into the push rod of the prop near the ball and socket joint supporting the cap. According to a preferred embodiment of the invention, the bar is fitted n the cap by means of an adjustable mechanism permitting the intro. duction as desired of an initial tension capable of compensating any asymmetry in the distribution of the masses of the cap or to absorb the effects of unbalanced weight when the seam has a large angle of tilt.

Reference should now be made to the accompanying drawings in which:

FIG. 1 is a diagram showing the manner in which a pit prop operates.

FIG. 2 shows an alternative where one or more shoes are provided on the sides of the caps to give guidance thereof.

FIG. 3 is an end view of a cap mounted on the top of a prop and provided with an automatic centering device according to the invention.

FIG. 4 is a section taken on the lines IV-IV of FIG. 3.

FIG. 5 corresponds to FIG. 4 and shows the operation of the flexion bar.

FIG. 6 is an end view showing the bar working in torsion and adjusted so as to exert an initial tension on the cap.

FIG. 7 is a partial section taken on the line VII-VII (FIG. 4) showing on a larger scale the fitting of the torsion bar in the push rod of the jack.

FIG. 1 shows a mine working having a comparatively heavy slope, the roof of which is supported by a hydraulic prop A which may be incorporated or not in a progressive supporting means. The prop A is locked against the floor by a sole 1 and against the roof by a cap 2. It rests on the sole 1 by a ball and socket joint 3, whilst its 'push rod A also ends in a ball 5. The latter is supported on the spherical interior of a socket 6 welded to the interior of the cap 2.

When the prop A is placed in position, it is arranged perpendicularly to the sole 1 and the cap 2 as shown in full lines in FIG. 1. Eventually relative movement of the floor and roof produces a tilt of the prop A between the sole 1 and the cap 2, as shown in broken lines in FIG. 1 in which the tilt is greatly exaggerated. In fact, the amplitude of movement of the prop A at the ball and socket joints 3 and 5 does not exceed a few degrees.

When the prop A is released, for example, to displace it in the case of progressive support, it is important to ensure its centering on the sole 1 automatically (devices are known capable of ensuring this operation) and to return the cap 2 to a position perpendicular to the rod 4. The invention concerns a device capable of automatically re-centering the cap on the ball and socket joint 5 of the rod 4 as soon as the prop A is disengaged.

A radially extending blind bore 7 is pierced in the side of the rod 4 near the ball 5, in which bore 7 the end 8a of a bar 8 having a square section is engaged. In principle, in order to ensure the fitting of the end 8a in the rod 4, it would be possible to provide a blind bore 7 having a square cross-section similar to that of the bar 8. In practice, since it is difficult to pierce a blind bore having a square cross-section, the bore 7 is given a circular section the diameter of which is almost equal to the length of the diagonal defined by the section of the bar 8. The part of the rod 4 concerned is surrounded by a ring 9 provided with a groove 10 the two edges of which are parallel and separated by a space 11 equal to the side of the square section of the bar 8.

The bar 8 passes freely through a lateral perforation 12 formed in a skirt 13 which rigidly connects the socket 6 to the body of the cap 2.

The other end 81) of the bar 8 also passes freely through a guide perforation 14 provided in a vertical rib 15 located within the cap to which it is connected. The end 8b is rigidly fitted in one end portion of an adjustment strip 16 the free end of which is provided with a perforation 17. The latter is made to coincide with any one of the perforations of a series disposed in an arc of a circle across the rib 15, round the bar 8. In the embodiments shown in FIGS. 3 and 6, these perforations in the rib 15 are shown as three in number, i.e., a centre perforation 18 and two end perforations 19 and 26 When the perforation 17 of the strip 16 is opposite one of the three perforations 18, 19 or 20, a fixing spike (not shown) is engaged therein to secure the end 8b of the bar 8 on the cap 2.

It is assumed that when the strip 16 is backed to the centre perforation 18, the cap 2 remains perpendicular to the push rod of the prop A, when the bar 8 is in the condition of rest, i.e., without any tension (case shown in FIG. 3).

The operation of the device is as follows:

If the prop A is freed as shown in FIGS. 3 and 4, it will be seen that the bar 8, which works in flexion and torsion, tends to return the cap 2 automatically perpendicular to the push rod 4. Consequently if the prop is used initially in this position, relative movement of the floor and roof of a seam causes a tilt of the cap 4 in the longitudinal direction (FIG. 5), the bar 8 bends and tends to return the cap 2 resiliently to its initial position relatively to the rod 4, as soon as the prop is disengaged. Similarly, if the prop position change caused by the movement of the soil corresponds to a transverse rocking movement of the cap 2 in the direction shown in FIG. 3 by the arrow 21, it will be seen that the bar 8 acts in torsion and automatically returns the cap 2 to its original position as soon as the propA is disengaged.

In certain cases and particularly when the seam has a heavy tilt, or when it is necessary to mount one or more shoes such as 22 (FIG. 2) on the cap 2 to ensure location of the caps relatively to each other, there is a resultant torque on the cap 2 which tends to make it swing transversely, in the direction shown in FIG. 6 by the arrows 23; this action is then compensated by coupling the strip 16 with the perforation 19 of the rib 15. In this case, when the prop is being locked against the roof, the forces exerted on the cap 2 cause pre-stressing by torsion to appear in the bar 8, which are balanced when the cap 2 is practically perpendicular to the push rod 4.

In the same manner the perforation 20 is used to couple to the strip 16 when it is desired to produce an initial tension in the opposite direction.

-It will be understood that the automatically centering device of the present invention has the advantages of minimum space requirements, absolute reliability in operation, possibility of simple control by adjustment of the strip 16 and locking of the cap 2 against the roof under the best conditions.

The above description is given only by way of example bodies which may be assembled so as to form a single prop. For example, if the cap 2 is carried simultaneously by two prop bodies A, it is possible to fit only one of them with a torsion and fiexion bar 8, the sole and the cap common to the assembly of the prop thus ensuring the automatic re-centering of the cap on the second prop body.

We claim:

1. A pit prop with a self-centering cap, comprising a hydraulically operated prop body, a push rod extending from said body, an elongated cap supported on said push rod, a ball and socket joint interconnecting said rod and said cap, and a torsion and fiexion bar fastened at one end to said rod near its ball end, and at the other end to said cap and extending parallel to the lengthwise direction of said cap.

2. A pit prop as recited in claim 1 characterised in that said torsion and flexion bar is fitted at the end remote from said ball joint with an adjusting strip, an adjustment plate on said cap defining a plurality of holes, and means for locating and fastening the free end of said strip in any one of said holes.

3. A pit prop as recited in claim 1 in which said torsion and flexion bar is fastened to said push rod by forming the bar of square section, inserting it in a round blind bore in said bar, and fixing it therein by means of a ring fastened to said push rod, said ring defining a slot receiving said square section bar.

4. A pit prop as recited in claim 1 characterised in that the ball of said ball and socket joint is formed on the end of said push rod, and the socket is fastened to said cap.

References Cited FOREIGN PATENTS 1,216,224 5/1966 Germany. 1,230,746 12/1966 Germany.

ROY D. FRAZIER, Primary Examiner.

FRANK DOMOTOR, Assistant Examiner. 

